DNA microarray hybridization is used to identify different viruses and viral strains. Hybridization with generic microchips (microarrays containing all possible hexameric oligonucleotides) can discrimination between point mutants quantify their contents in viral stocks. Comparison of hybridization patterns of vaccine strain and its neurovirulent revertant using a chip with 4096 elements identifies a few oligonucleotides, the binding of which is affected by the mutation. Quantification of fluorescence intensity of these elements can assess the relative abundance of the mutants. Another kind of oligonucleotide microchip containing probes specific for individual viruses and for groups of related viruses is used to identify viruses in biological samples and to classify them. This method can be used to test the identity and stability of vaccine viruses, to identify adventious agents, and to search for emerging and re-emerging pathogens.